Green power: Sustainable building techniques and technologies

June 30, 2008 |

Green power: Sustainable building techniques and technologies(Continued from p. 70 of the July 2008 issue of BD+C)

GEOTHERMAL HEAT PUMP SYSTEMS

As an established and proven source of renewable energy, geothermal building technologies, in particular heat-pump systems, are promoted by green building advocates the world over. The U.S. Environmental Protection

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This program is registered with the AIA/CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.

Agency (EPA) credits geothermal heat pumps with providing the best life cycle cost payback, the lowest CO2 emissions, and the lowest overall environmental impact, as compared to all other heating/cooling systems. Now that the cost of natural gas and oil has shot up so significantly, geothermal has become an even more serious consideration for building projects, say many building experts.

“The volatility of these utilities has led many building owners to seek a more stable form of energy, cost-wise, to heat and cool their facilities,” says Thomas Carson, P.E., manager of mechanical engineering with the A/E firm Schemmer, based in Omaha, Neb. “Geothermal is also riding a wave of notoriety due to the mainstream push to become green.”

Geothermal technologies essentially use the relatively constant temperatures within the earth’s crust to heat buildings in the winter and cool them in summer. Heat pumps and other techniques, such as excavating and building below ground, allow building owners to draw out the stored energy for practical uses. The heating and cooling power is essentially free; all one has to do is tap into it. According to Matt Ebejer, P.E., vice president and healthcare market focus leader for Syska Hennessy Group, Los Angeles, using geothermal systems confers the following benefits:

• Reduced loads on the building’s electrical system.

• Reduction of natural gas service to a building.

• Elimination of costly boiler and chiller equipment and rooms.

• Decreased need for rooftop equipment and related screening and structure to handle the equipment.

• Free domestic hot water, as a geothermal waste product, when the system is in the cooling mode.

Furthermore, the overall positive holistic impact of geothermal systems on the entire building can be significant. This can include occupant health benefits, reduced life cycle costs, and overall programmatic efficiencies—although these factors have yet to be fully documented and quantified.

“To date we have not been able to get a full grasp of the actual cost difference [of using geothermal systems] as they pertain to the complete building,” says Don Penn, P.E., a certified geothermal designer (CGD) and president of Image Engineering Group in Grapevine, Texas. For example, the building envelope, structural systems, electrical load requirements, and square footage reductions have never been evaluated. “Studies typically just include one mechanical system in comparison to one or more other choices, not a holistic evaluation,” says Penn.

Getting in the LoopAs noted, the brilliance of geothermal systems is in their ability to harness and convey the earth’s constant temperature.

Geothermal payback in the Big Apple

As the region’s first geothermal installation in a building open to the public, Manhattan’s Center for Architecture—home to the American Institute of Architects New York Chapter (AIANY), in addition to five other architecture and engineering associations—is reaping the benefits of energy and operational savings.

When the Center decided to move to its current location in Greenwich Village, the initial decision to go with earth energy wasn’t so simple.

“We looked very hard at first costs, since the project was on a bare-bones budget of $200 per square foot, and the well drilling for the two geothermal wells alone represented 3% of the construction budget, the largest single line item,” recalls Rick Bell, FAIA, executive director of AIA New York’s Center for Architecture. “We determined that the initial costs for the geothermal system, based on our programming projections, would be paid back in approximately three years, so we decided to proceed.”

Ultimately, financial and technical support from the New York State Energy Research Development Authority essentially erased the cost differential from a conventional HVAC installation.

The system’s two parallel geothermal wells extend 1,260 feet into bedrock beneath the building—deeper than the Empire State Building is tall—circulating 55º F water for heating and cooling. The water is drawn and then pumped to heat exchanger units inside the building’s mechanical room. The heat exchanger then either extracts heat or transfers it to the well water, depending on whether it’s a heating or cooling day. Next, the water is circulated back to the well while the tempered water is sent to nine heat pumps located in mechanical rooms throughout the three floors the Center occupies.

“We sized the geothermal system to be able to supply the cooling and heating needs of the entire eight-story building,” even though the Center occupies only the ground floor and two basement levels,” says Bell. “The number of wells, and their depth, was determined by engineering calculations that went beyond our projected needs for opening day, whether or not we ever occupy more space within the building.”

“Quite simply, geothermal systems take heat from the earth, transfer that heat to a refrigerant, and then distribute the heat into the structure with a forced-air or hydronic system,” explains J. Ramon, a contractor with Geothermal Design Associates, Fort Wayne, Ind. “In cooling, geothermal systems take heat from the structure, transfer the heat to the refrigerant, then transfer the heat back to the water or loop fluid.” In order to anchor the geothermal system to the earth, three different systems can be employed:

• Open-loop systems pump well water to the geothermal unit, where heat is either taken from it for heating purposes or put back into it for cooling.

• Water loops operate using water from a nearby pond or lake; ocean or bay water can also be used in some cases.

“Pond or lake loops may indeed be the best system available,” says Ramon. “They have the benefit of low installation costs in addition to the benefits of a closed loop. Also, pond and lake loops typically have more mild operating temperatures.”

The main benefit of closed-loop systems is that they require very little maintenance. However, due to excavation costs, they tend to be more expensive to install than open-loop types. “Typically, in certain parts of the country, such as the Midwest, loop systems are installed in a horizontal configuration, but in other parts of the country, where digging is more difficult or expensive, vertical loops are used,” Ramon clarifies. Vertical loops may be excavated or drilled.

Before determining whether a specific site is suitable for geothermal, a test bore must be performed. “What’s more important than the geographic region or climate is the soil composition beneath the ground,” says Carson. “Ground types that provide good conduction of heat from the wells are best suited for geothermal, whereas ground that is rocky and difficult to drill is generally a poor candidate.”

New Developments in Earth EnergyEven though the key to the effectiveness of geothermal technology is its field infrastructure, this is generally a pricey first-cost item that often knocks heat pumps right out of the project budget. However, a few new system concepts are making the front-end work more affordable.

“Until about a year ago, a typical stand field consisted of six-inch bores ranging from 150 feet to 350 feet deep,” says Syska Hennessy’s Ebejer. “Each bore would be provided with a one-inch U-tube pipe and could only provide from 1 to 2 tons of heating or cooling.” Now, a new pipe created for geothermal applications has been shown to work well with four-inch bores, yielding 3-5 tons of cooling per bore. This new pipe promises to reduce installation costs by about a third.

“Another development is that manufacturers are producing equipment that is substantially more energy efficient than conventional systems,” says Image Engineering Group’s Penn. “The best chiller/air-handler pump system uses about 1.1 kilowatts per ton, whereas the new hi-efficiency geothermal equipment is ranging from 0.65 to 0.70 kW per ton.”

Many industry observers and green design practitioners would like to see more resources pumped into geothermal R&D. Fortunately, a number of government and academic research projects are also improving the technology. The U.S. Department of Energy, for example, is supporting numerous ongoing national laboratory research programs studying enhanced geothermal system development, as well as component-level improvements to downhole diagnostics, evaporative cooling, mixed binary working fluids, and corrosion-resistant coatings .

Tonya Boyd, assistant director of the Geo-Heat Center at the Oregon Institute of Technology in Klamath Falls, reports that her group is “looking at different ways of installing the loops in horizontal systems, like using horizontal boring systems, instead of digging trenches, and combining geothermal and solar thermal systems in northern climates where the heat in the ground is replenished by the solar thermal in the summer along with the cooling cycle of the geothermal system.”

The U.S. Leads the Way

The United States is among the most active countries in terms of direct-use geothermal applications and overall installed capacity. The majority of U.S. geothermal activity has been in the West, particularly in Nevada and California, where geothermal power generation provides around 6% of each state’s energy demand.

Construction workers dig holes for geothermal pipes at a housing development installation.

Federal tax incentives passed into law in 2005 under EPAct 2005, plus the newly legislated Renewable Portfolio Standards in a number of western states, are driving growth of geothermal development. According to the U.S. Geothermal Energy Association, 61 large new geothermal projects were under way as of 2006.

Not surprisingly, many say there is considerably more untapped potential for geothermal. According to a recent Massachusetts Institute of Technology study, current system types could yield millions of gigawatts of geothermal energy, providing 10% of U.S. energy needs by 2050, if sufficient resources were invested in development.

“In spite of its enormous potential, the geothermal option for the United States has been largely ignored. In the short term, R&D funding levels and government policies and incentives have not favored growth of the U.S. geothermal capacity,” states the DOE-sponsored MIT report, “The Future of Geothermal Energy,” http://www1.eere.energy.gov/geothermal/future_geothermal.html.

Although it has a long way to go before being signed into law, the National Geothermal Initiative Act of 2007, now in Senate committee, could potentially ease things in the right direction. The bill seeks to invest $75 million in

Beware of short looping

Matt Ebejer, PE, vice president and healthcare market focus leader for Syska Hennessy Group, Los Angeles, cautions against short looping, which can jeopardize the efficiency of a geothermal project.

“Short looping is not installing enough geothermal fields, so that the geothermal heat pump units operate at peak capacity all the time,” he explains. “The system heats and cools the building, but the equipment that was designed to operate at 0.70 kilowatts per ton operates at 0.9 kilowatts per ton because the loop field temperature is 90 F instead of the designed 70 F.”

To guard against such an eventuality, Ebejer advises that “the construction documents must tell the contractor exactly what the engineer wants, from bore size, depth of bore, spread spacing, type of grout, etc. The engineer cannot leave these items up to the contractor.”

geothermal technology development this year, and $110 million per year, from 2009 to 2013. The bill also aims to expand geothermal energy production from a handful of western states to at least 25 states nationwide.

Obstacles and Opportunities

Besides a need for additional funding and development, life cycle benefits often need to be prioritized over first costs for geothermal projects to be viable.

“We see the geothermal systems being more applicable in institutional-type facilities, 40- to 50-year buildings, where the owner is savvy about long-term life cycle costs,” says Penn, whose firm Image Engineering Group has designed more than 150 geothermal systems for K-12 school districts in Texas. Facilities designed for “the developer market where the buildings are for an investment to turn over in a few years, where first cost prevails, typically are not good candidates,” he adds.

Also built into that first cost are such expenses as permitting and inspection fees, and the hard-to-predict value of drilling, especially in cases where a few drilling firms have a monopoly on a particular local market. At the same time, Carson points out, “The number of specialty well-drilling contractors has grown in the past five years, and this has brought down the cost of drilling new well fields.”

Building designers and contractors also complain that even without discussing first cost, they experience resistance from owners, developers, and even local officials simply because these parties lack understanding about the benefits of geothermal technology and how it works. Some see this stumbling block even when working with some MEP engineers and financial institutions.

One other challenge comes from environmentalists: Though interested in the energy profile of the systems, they are concerned about the invasiveness of geothermal installations and operations. Do underground wells pose a significant threat to soils and the ecosystem generally? Ebejer notes that closed-loop systems have been shown not to affect the groundwater, and the EPA considers geothermal systems to be environmentally safe.

“After the borehole is drilled and the loops placed in the hole, the borehole is grouted to provide sanitary protection for a water supply by preventing leakage downward along the borehole,” adds the Oregon Institute of Technology’s Boyd. “Also, the grouting protects water-bearing formations by preventing the migration of water between aquifers, and will preserve the hydraulic characteristics of artesian formations and prevent leakage upward along the borehole.”

In addition to the environmental and energy-saving advantages, geothermal development also helps stimulate local economic activity, as opposed to purchasing energy from outside utilities or overseas suppliers. Although increased financial incentives and R&D will be necessary to more fully realize geothermal’s potential, many are optimistic. “I foresee geothermal use greatly increasing in the next few years,” predicts Ebejer. “As the cost of fossil fuels increases, an inexpensive source will be required, and geothermal offers that.”

WIND POWER FOR BUILDINGS

Wind is another environmentally friendly and cost-effective way to generate power. Wind energy is plentiful, renewable, and clean, and it can reduce greenhouse gas emissions by replacing conventional electricity. By the

While wind power is less common than PV installations, distributed wind energy is catching on. This dwelling has both solar power panels and wind generator, which charge a bank of batteries fed through a power inverter to deliver enough 120V AC to power the entire compound.

end of last year, wind-powered generators had a worldwide capacity of about 94 gigawatts—a mere 1% of the world’s electricity. But the supply of wind power has grown fivefold since the year 2000.

Since the 1980s, the modern wind turbine has been used for electricity generation of small facilities in conjunction with battery storage in remote areas. Grid-connected turbines in the 1-10 kW range can power entire light commercial structures and use grid energy storage to save power for peak use. Users of small-scale turbines who are off the grid must adapt to intermittent power or opt to use batteries, diesel, or photovoltaic diesel systems to supplement their turbines.

A consistent 10-12 mile per hour wind is ideal for using wind turbines. In urban, industrial, and commercial locations, where it is difficult to sustain a consistent amount of wind energy, smaller systems may still be used to run low-power equipment, such as parking meters or wireless Internet routers.

There are surprisingly few limitations on wind power in zoning codes and local laws on the use of wind power in urban areas, other than those related to height. One common obstacle, however, is local opposition to erecting wind turbines, says Preston Koerner, a lawyer, environmentalist, and creator of the online journal Jetson Green (www.jetsongreen.com). Residents are often concerned about cost, noise, or installation disturbances of wind turbines, which tend to be minimal as compared to other project types. Koerner remains optimistic, however: “It’s an innovation space,” he says. “A lot of money is going into clean technology right now, and we need it.”

Koerner and other experts point to a number of successful large-scale applications of commercial wind power outside the U.S., most notably the World Trade Center tower in Bahrain. New, state-of-the-art buildings in planning or under construction that will use wind power include the Pearl River tower in China, Core Tower in Florida, and the Clean Technology Tower in Chicago. Houston’s Discovery Tower will feature its own rooftop wind farm. With these developments, industry experts believe, the United States alone is poised to provide 20% of the world’s electrical grid by wind alone.

About the authorsC.C. Sullivan is a communications consultant and author specializing in architecture and construction. Barbara Horwitz-Bennett is a writer and contributor to construction industry publications.

Reed Business Information is a Registered Provider with the American Institute of Architects Continuing Education Systems. Credit earned on completion of this program will be reported to CES Records for AIA members. Certificates of Completion for non-AIA members are available on request.

This program is registered with the AIA/CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.

The report, “Spending Through the Roof,” says that apartment building owners pay an average of $3,400 a year to replace heat lost through the roof. In taller buildings, the cost can be more than $20,000 a year. Illustration: Urban Green Council